摘要:

The possibility of determining the frame size of a motor on economic instead of physical grounds is first discussed, and a basis is laid down-for economic comparisons. The capital and working charges are considered in turn, and in connection with the latter the efficiency of a shunt motor when suitably under-run is examined. Applying this method to the case where ⅛ h.p. at 1000 r.p.m. is required, the economical position is indicated for various conditions of service and prices of energy, and it is found that a ⅕-h.p. or ¼-h.p. frame is preferable in all but exceptional cases. Applying the method to sizes ranging from ¼ h.p. to 15 h.p. similar results are obtained, and it is found that the usual physical criteria are only satisfactory as a sole basis of choice when energy is exceptionally cheap or hours of service are short. The possible extension of the method and the effect of various changes are briefly reviewed.

DOI:10.1049/jiee-1.1924.0118

出版商:IEE    

年代:1924

数据来源: IET

摘要:

The current-carrying capacity of bare copper and aluminum conductors is limited by the heating effects produced by the current. The dissipation of this heat is a function of the temperature elevation above the surrounding air, the size of the conductor, and the intrinsic condition of the surface. A cooling-curve method is described which was used in determining the coefficient of heat emissivity for a series of small sample lengths of round and flat copper and aluminium conductors of various sizes and surface conditions. This was checked by the direct electrical heating of longer lengths, which showed the two methods to be in close agreement. Tables for the current-carrying capacity of copper and aluminium busbars have been deduced from the constants obtained and are given in the paper.

DOI:10.1049/jiee-1.1924.0119

出版商:IEE    

年代:1924

数据来源: IET

摘要:

A generalized theorem is given of which the well-known three-ray star-mesh transformation is a particular case. The formula is of a simple nature, and a great saving of labour results from its use. Three examples of application of the theorem follow: (1) To find the effective conductance between two points in a complicated network; (2) to find the effect of earth admittances on the balance of a Wheatstone bridge; and (3) to simplify the capacity network in the four-wire telephone cable and obtain the effective unbalance capacity.

DOI:10.1049/jiee-1.1924.0120

出版商:IEE    

年代:1924

数据来源: IET

摘要:

Considerable interest has recently been shown in the complete elimination of all harmonics from the induced E.M.F. wave-form of an alternator. The methods usually employed in practice for the purification of the wave-shape fall into two classes: (a) in which certain harmonics are removed by proper choice of the characteristics of the armature winding, and (b) in which an endeavour is made to attain the desired end by producing a sinusoidally distributed flux round the air-gap. The object of the present paper is to give the theory of a commonly used method of the second class, in which the reluctance of the gap from point to point is adjusted to the value proper to the sinusoidal flux by shaping the pole-face to give a gap of varying length, longer at the tip than at the centre of the pole. The problem is solved for the case of a smooth-core armature, or for one in which the slots have been closed by means of magnetic wedges, such as would be used in a wave-form standard. Flat and circular armatures with any number of poles are dealt with, the shape of the pole-shoes and the permeance of the gap being determined in each case. The paper concludes with a numerical example illustrating the theory given in the text.

DOI:10.1049/jiee-1.1924.0122

出版商:IEE    

年代:1924

数据来源: IET

DOI:10.1049/jiee-1.1924.0123

出版商:IEE    

年代:1924

数据来源: IET

摘要:

The importance of foreign markets for the electrical industry of Great Britain and the characteristics of Russia as a prospective market for electrical goods are discussed, a brief account being given of general Russian economics.The possibilities of electrification in Russia, and projects of various electrification schemes are then described, and an outline of results achieved and work done is included.

DOI:10.1049/jiee-1.1924.0124

出版商:IEE    

年代:1924

数据来源: IET

摘要:

The paper discusses interference between power circuits and telegraph and telephone circuits. A distinction is made between “radiation” and “induction.” The former cause produces both electric and magnetic effects and is used in radio-telegraphy. The conductivity of the earth, which is not a homogeneous body, should be taken into account. Experiment, however, shows that in radio work we can get approximate solutions by assuming that the earth is a non-conductor and that its inductivity is unity. Making this assumption, it is shown that the intensity of the “radiation” field in simple cases falls off inversely as the distance and inversely as the wave-length. On this assumption also the intensity of the induction field, whether electrostatic or electromagnetic, obeys this law in a few cases. It is pointed out that a balanced three-phase system produces both electric and magnetic rotary fields in its neighbourhood, the amplitudes of which fall off according to the inverse square of the distance. A three-phase four-wire system, however, may produce serious interference with telephone systems even when the phases are balanced. In an appendix an easy method of finding the numerical value of the mutual capacity coefficient between two spheres is given.

DOI:10.1049/jiee-1.1924.0126

出版商:IEE    

年代:1924

数据来源: IET

DOI:10.1049/jiee-1.1924.0127

出版商:IEE    

年代:1924

数据来源: IET

摘要:

This paper is intended, not to give a detailed consideration of a subject upon which it is difficult to theorize, but rather to bring to the notice of engineers, who are mostly engaged on high-power plants, the achievements of a little-known department of all railway companies, the object of the department being to protect moving and stationary vehicles. The paper gives a very brief description of the evolution of the lock-and-block system of signalling and the uses of the track circuit as now employed on the Midland section of the London, Midland and Scottish Railway.

DOI:10.1049/jiee-1.1924.0128

出版商:IEE    

年代:1924

数据来源: IET

摘要:

For the explanation of the variable errors encountered chiefly at night on radio direction-finders, modern theory implies the reception of waves arriving at an appreciable angle of elevation and polarized so that the magnetic field has a horizontal component in the plane of propagation. Previous experimenters have shown that such abnormally polarized waves can be radiated from certain kinds of aerials when situated at a considerable distance from the earth's surface, as in the case of an aeroplane transmitter, and that such waves when arriving at the earth's surface can produce very appreciable errors on a radio direction-finder. The experiments described in the present paper were carried out to determine to what extent the emission of these abnormally polarized waves by aerials of different shapes from a ground transmitting station was responsible for the frequent occurrence of variable “night” errors at a ground direction-finding station. It is concluded that the frequency and magnitude of these errors are independent of the shape of the transmitting aerial, within the limits of this investigation, and that the use of a source of radiation which is, as far as possible, only polarized in the normal manner, in no way diminishes the night effects generally experienced.

DOI:10.1049/jiee-1.1924.0129

出版商:IEE    

年代:1924

数据来源: IET